cheatsheet of boost.xpressive w/ semantic actions

xpr_chatsheet.cpp

#include <iostream>
#include <string>
#include <stack>
#include <functional>
//xpressiveのうち、staticのためのヘッダ
#include <boost/xpressive/xpressive_static.hpp>
// セマンティックアクションのためのヘッダ
#include <boost/xpressive/regex_actions.hpp>

namespace xpr = boost::xpressive;
std::stack<int> operandStack; //計算用スタック
struct Operand { // オペランド(終端子)を扱う関数の実体。意図的にはdouble→void。多態は無理っぽい
	typedef void result_type;
	void operator()(const int i) const{
		operandStack.push(i);
	};
};


struct Operator { // オペレータを扱う関数の実体
	typedef void result_type;
	void operator()(std::function<int(int, int)> f) const{
			double i, j;
			i = operandStack.top();
			operandStack.pop();
			j = operandStack.top();
			operandStack.pop();
			operandStack.push(f(i, j));
	};
};
int main() {

  const xpr::function<Operand>::type rcvOperand = {{}};
  const xpr::function<Operator>::type rcvOperator = {{}};

  xpr::sregex digit, expr, term, op1, op2;

  using namespace boost::xpressive;

	digit = (+_d)[rcvOperand(as<int>(_))] ;
	term = (digit | (as_xpr('(') >> *_s >> by_ref(expr) >> ')')) >> *_s ;
	op1 = term >> *(((s1 = as_xpr('*') | '/') >> *_s >> term)[rcvOperator(((as<char>(s1) == '*')? std::multiplies<int>: std::divides<int>))]);
	op2 = op1 >> *(((s1 = as_xpr('+') | '-' ) >> *_s >> op1)[rcvOperator(((as<char>(s1) == '+')? std::plus<int>: std::minus<int>))]);
	expr = bos >> *_s >> op2 >> eos;

	smatch match;

	std::string str("1 * (2 + 3) + 4 * 6"); //->29

	if(regex_match(str, match, expr)){
		std::cout <<
			"Ans: " << operandStack.top() << std::endl;
	}

	return 0;
}